Signaling guard interval capability in a communication system

ABSTRACT

In a wireless network in which communication devices are configured to use a first guard interval between symbols or a second guard interval between symbols, wherein the first guard interval has a length shorter than a length of the second guard interval, a field in a data unit received from a communication device is analyzed to determine a set of one or more modulation and coding schemes (MCSs) supported by the communication device and to determine whether one or more MCSs in the set of one or more MCSs is supported by the communication device when using the first guard interval. One MCS in the set of one or more MCSs and the first guard interval is utilized a) when communicating with the communication device, and b) when it is determined that the one MCS is supported by the communication device when using the first guard interval.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/102,727, now U.S. Pat. No. 8,665,908, entitled “Signaling GuardInterval Capability in a Communication System,” filed May 6, 2011, whichclaims the benefit of U.S. Provisional Patent Application No.61/333,690, filed on May 11, 2010. Both of the applications referencedabove are hereby incorporated by reference herein in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to communicating device capabilities between devicesin a wireless network.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Development of wireless local area network (WLAN) standards such as theInstitute for Electrical and Electronics Engineers (IEEE) 802.11a,802.11b, 802.11g, and 802.11n Standards, has improved single-user peakdata throughput. For example, the IEEE 802.11b Standard specifies asingle-user peak throughput of 11 megabits per second (Mbps), the IEEE802.11a and 802.11g Standards specify a single-user peak throughput of54 Mbps, and the IEEE 802.11n Standard specifies a single-user peakthroughput of 600 Mbps. Work has begun on a new standard, IEEE 802.11ac,that promises to provide even greater throughput.

SUMMARY

In one embodiment, a method for generating a data unit for transmissionin a wireless network is disclosed. Communication devices in thewireless network are configured to use a first guard interval betweensymbols or a second guard interval between symbols, wherein the firstguard interval has a length shorter than a length of the second guardinterval. The method includes generating a field to indicate a set ofone or more modulation and coding schemes (MCSs) supported by a firstdevice in the wireless network and to indicate whether each of the oneor more MCSs is supported when using the first guard interval. Themethod also includes generating a data unit to include the field andcausing the data unit to be transmitted to a second device in thewireless network.

In another embodiment, an apparatus for use in a wireless network isdisclosed. The wireless network is configured to use a first guardinterval between symbols or a second guard interval between symbols,wherein the first guard interval has a length shorter than a length ofthe second guard interval. The apparatus comprises a wireless networkinterface configured to generate a field to indicate a set of one ormore modulation and coding schemes (MCSs) supported by the wirelessnetwork interface and to indicate whether each of the one or more MCSsis supported when using the first guard interval. The wireless networkinterface is further configured to generate a data unit to include thefield and cause the data unit to be transmitted to another device in thewireless network.

In yet another embodiment, a method for determining capabilities of acommunication device in a wireless network is disclosed. The wirelessnetwork is configured to use a first guard interval between symbols or asecond guard interval between symbols, wherein the first guard intervalhas a length shorter than a length of the second guard interval. Themethod includes analyzing a field in a data unit received from acommunication device to determine a set of one or more modulation andcoding schemes (MCSs) supported by the communication device and todetermine whether one or more MCSs in the set of one or more MCSs issupported by the communication device when using the first guardinterval. Additionally, the method includes utilizing i) one MCS in theset of one or more MCSs and ii) the first guard interval a) whencommunicating with the communication device and b) when it is determinedthat the one MCS is supported by the communication device when using thefirst guard interval.

In still another embodiment, an apparatus for use in a wireless networkis disclosed. The wireless network is configured to use a first guardinterval between symbols or a second guard interval between symbols,wherein the first guard interval has a length shorter than a length ofthe second guard interval. The apparatus comprises a wireless networkinterface configured to analyze a field in a data unit received from acommunication device to determine a set of one or more modulation andcoding schemes (MCSs) supported by the communication device and todetermine whether one or more MCSs in the set of one or more MCSs issupported by the communication device when using the first guardinterval. The wireless network interface is further configured toutilize i) one MCS in the set of one or more MCSs and ii) the firstguard interval when communicating with the communication device and whenit is determined that the one MCS is supported by the communicationdevice when using the first guard interval.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN) that utilizes techniques for communicating capabilities betweendevices, according to an embodiment.

FIG. 2 is a block diagram of an example physical layer (PHY) processingunit, according to an embodiment.

FIG. 3 is a diagram of an example orthogonal frequency divisionmultiplexing (OFDM) symbol, according to an embodiment.

FIG. 4 is a diagram of a field included in an example data unit,according to an embodiment.

FIG. 5 is a flow diagram of an example method for generating a data unitto communicate capabilities with other communication devices in awireless network, according to an embodiment.

FIG. 6 is a flow diagram of an example method 600 for determiningcapabilities of a communication device, according to an embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. According to an embodiment,symbols transmitted by the AP include guard intervals to prevent orminimize intersymbol interference at the receiver caused by multipathpropagation in the communication channel. The length of the guardinterval needed to mitigate interference generally depends on the delayspread of the particular channel being utilized. Consequently, in someembodiments and/or scenarios, the guard interval utilized by the AP is along guard interval (LGI), while in other embodiments and/or scenarios,the guard intervals utilized is a short guard interval (SGI). The shortguard interval has an advantage of reducing idle time between symbolsand thus increasing transmission data rate. However, in some situations,the increased data rate associated with the shorter guard interval isnot supported by a particular client station, and in these situationsthe longer guard interval needs to be utilized even if the delay spreadof the channel allows for a shorter guard interval to be used.Therefore, a client station, in establishing communication with an AP,communicates to the AP data rate capabilities of the client station invarious scenarios and/or embodiments. For example, in an embodiment, theclient station communicates to the AP information that allows the AP todetermine if a short guard interval is supported by the client stationfor a particular channel bandwidth and/or a particular modulation andcoding scheme (MCS). In an embodiment, the AP utilizes this informationto determine the proper guard interval based on the bandwidth and MCSbeing utilized for communicating with the client station. Similarly, theAP communicates to the client station data rate capabilities of the APin other various scenarios and/or embodiments. Additionally, a firstclient station communicates to a second client station data ratecapabilities of the first client station in other various scenariosand/or embodiments.

FIG. 1 is a block diagram of an example embodiment of a wireless localarea network (WLAN) 10 that utilizes techniques described herein forcommunicating capabilities among devices, according to an embodiment. AnAP 14 includes a host processor 15 coupled to a network interface 16.The network interface 16 includes a medium access control (MAC)processing unit 18 and a physical layer (PHY) processing unit 20. ThePHY processing unit 20 includes a plurality of transceivers 21, and thetransceivers are coupled to a plurality of antennas 24. Although threetransceivers 21 and three antennas 24 are illustrated in FIG. 1, the AP14 can include different numbers (e.g., 1, 2, 4, 5, etc.) oftransceivers 21 and antennas 24 in other embodiments. In one embodiment,the MAC processing unit 18 and the PHY processing unit 20 are configuredto operate according to a first communication protocol (e.g., the IEEE802.11ac Standard, now in the process of being standardized). The firstcommunication protocol is also referred to herein as a very highthroughput (VHT) protocol. In another embodiment, the MAC processingunit 18 and the PHY processing unit 20 are also configured to operateaccording to at least a second communication protocol (e.g., the IEEE802.11n Standard, the IEEE 802.11a Standard, etc.).

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 can includedifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. At least one of the client stations25 (e.g., client station 25-1) is configured to operate at leastaccording to the first communication protocol.

The client station 25-1 includes a host processor 26 coupled to anetwork interface 27. The network interface 27 includes a MAC processingunit 28 and a PHY processing unit 29. The PHY processing unit 29includes a plurality of transceivers 30, and the transceivers 30 arecoupled to a plurality of antennas 34. Although three transceivers 30and three antennas 34 are illustrated in FIG. 1, the client station 25-1can include different numbers (e.g., 1, 2, 4, 5, etc.) of transceivers30 and antennas 34 in other embodiments.

In an embodiment, one or all of the client stations 25-2, 25-3 and 25-4,have a structure the same as or similar to the client station 25-1. Inthese embodiments, the client stations 25 structured the same as orsimilar to the client station 25-1 have the same or a different numberof transceivers and antennas. For example, the client station 25-2 hasonly two transceivers and two antennas, according to an embodiment.

In various embodiments, the PHY processing unit 20 of the AP 14 isconfigured to generate data units conforming to the first communicationprotocol. The transceiver(s) 21 is/are configured to transmit thegenerated data units via the antenna(s) 24. Similarly, thetransceiver(s) 24 is/are configured to receive the data units via theantenna(s) 24. The PHY processing unit 20 of the AP 14 is configured toprocess received data units conforming to the first communicationprotocol, according to an embodiment.

In various embodiments, the PHY processing unit 29 of the client device25-1 is configured to generate data units conforming to the firstcommunication protocol. The transceiver(s) 30 is/are configured totransmit the generated data units via the antenna(s) 34. Similarly, thetransceiver(s) 30 is/are configured to receive data units via theantenna(s) 34. The PHY processing unit 29 of the client device 25-1 isconfigured to process received data units conforming to the firstcommunication protocol, according to an embodiment.

FIG. 2 is a block diagram of an example PHY processing unit 200configured to operate according to the VHT protocol, according to anembodiment. Referring to FIG. 1, the AP 14 and the client station 25-1,in one embodiment, each include a PHY processing unit such as the PHYprocessing unit 200.

The PHY unit 200 includes a scrambler 204 that generally scrambles aninformation bit stream to reduce the occurrence of long sequences ofones or zeros, according to an embodiment. In another embodiment, thescrambler 204 is replaced with a plurality of parallel scramblerslocated after an encoder parser 208. In this embodiment, each of theparallel scramblers has a respective output coupled to a respective oneof a plurality of FEC encoders 212. The plurality of parallel scramblersoperate simultaneously on a demultiplexed stream. In yet anotherembodiment, the scrambler 204 comprises a plurality of parallelscramblers and a demultiplexer that demultiplexes the information bitstream to the plurality of parallel scramblers, which operatesimultaneously on demultiplexed streams. These embodiments may beuseful, in some scenarios, to accommodate wider bandwidths and thushigher operating clock frequencies.

The encoder parser 208 is coupled to the scrambler 204. The encoderparser 208 demultiplexes the information bit stream into one or moreencoder input streams corresponding to one or more FEC encoders 212. Inanother embodiment with a plurality of parallel scramblers, the encoderparser 208 demultiplexes the information bit stream into a plurality ofstreams corresponding to the plurality of parallel scramblers.

Each encoder 212 encodes the corresponding input stream to generate acorresponding encoded stream. In one embodiment, each FEC encoder 212includes a binary convolutional encoder. In another embodiment, each FEC212 encoder includes a binary convolutional encoder followed by apuncturing block. In another embodiment, each FEC encoder 212 includes alow density parity check (LDPC) encoder. In yet another embodiment, eachFEC encoder 212 additionally includes a binary convolutional encoderfollowed by a puncturing block. In this embodiment, each FEC encoder 212is configured to implement any of: 1) binary convolutional encodingwithout puncturing; 2) binary convolutional encoding with puncturing; or3) LDPC encoding.

A stream parser 216 parses the one or more encoded streams into one ormore spatial streams for separate interleaving and mapping intoconstellation points. Corresponding to each spatial stream, aninterleaver 220 interleaves bits of the spatial stream (i.e., changesthe order of the bits) to prevent long sequences of adjacent noisy bitsfrom entering a decoder at the receiver. Also corresponding to eachspatial stream, a constellation mapper 224 maps an interleaved sequenceof bits to constellation points corresponding to different subcarriersof an OFDM symbol. More specifically, for each spatial stream, theconstellation mapper 224 translates every bit sequence of length log2(M) into one of M constellation points. The constellation mapper 224handles different numbers of constellation points depending on the MCSbeing utilized. In an embodiment, the constellation mapper 224 is aquadrature amplitude modulation (QAM) mapper that handles M=2, 4, 16,64, 256, and 1024. In other embodiments, the constellation mapper 224handles different modulation schemes corresponding to M equalingdifferent subsets of at least two values from the set {2, 4, 16, 64,256, 1024}.

In an embodiment, a space-time block coding unit 228 receives theconstellation points corresponding to the one or more spatial streamsand spreads the spatial streams to a greater number of space-timestreams. In some embodiments, the space-time block coding unit 228 isomitted. A plurality of CSD units 232 are coupled to the space-timeblock unit 228. The CSD units 232 insert cyclic shifts into all but oneof the space-time streams (if more than one space-time stream) toprevent unintentional beamforming. For ease of explanation, the inputsto the CSD units 232 are referred to as space-time streams even inembodiments in which the space-time block coding unit 228 is omitted.

A spatial mapping unit 236 maps the space-time streams to transmitchains. In various embodiments, spatial mapping includes one or moreof: 1) direct mapping, in which constellation points from eachspace-time stream are mapped directly onto transmit chains (i.e.,one-to-one mapping); 2) spatial expansion, in which vectors ofconstellation point from all space-time streams are expanded via matrixmultiplication to produce inputs to the transmit chains; and 3)beamforming, in which each vector of constellation points from all ofthe space-time streams is multiplied by a matrix of steering vectors toproduce inputs to the transmit chains.

Each output of the spatial mapping unit 236 corresponds to a transmitchain, and each output of the spatial mapping unit 236 is operated on byan IDFT unit 240 that converts a block of constellation points to atime-domain signal. Outputs of the IDFT units 240 are provided to GIinsertion and windowing units 244 that prepend, to each OFDM symbol, aguard interval (GI) portion, which is a circular extension of the OFDMsymbol in an embodiment, and smooth the edges of each symbol to increasespectral decay. Outputs of the GI insertion and windowing units 244 areprovided to analog and RF units 248 that convert the signals to analogsignals and upconvert the signals to RF frequencies for transmission.The signals are transmitted in a 20 MHz, a 40 MHz, an 80 MHz, a 120 MHz,or a 160 MHz bandwidth channel, in various embodiments and/or scenarios.

FIG. 3 is a diagram of an example OFDM symbol 300 generated by the PHYprocessing unit 200, according to an embodiment. The OFDM symbol 300includes a guard interval portion 302 and a data portion 304. Forexample, the guard interval comprises a cyclic prefix repeating an endportion of the symbol, according to an embodiment. Further, according toone embodiment, the guard interval portion 302 is either a short guardinterval or a long guard interval, depending on mode of transmission tobe utilized. In an embodiment, the short guard interval (SGI) has alength of 0.4 μs, and the long guard interval (LGI) has a length of 0.8μs guard interval. In an embodiment, the data portion 304 has a lengthof 3.2 μs. In other embodiments, other suitable lengths for the SGI, theLGI, and the data portion 304 are utilized. In some embodiments, the SGIhas a length that is 50% of the length of the LGI. In other embodiments,the SGI has a length that is 75% or less of the length of the LGI. Inother embodiments, the SGI has a length that is 50% or less of thelength of the LGI.

In an embodiment, the data rate of data units processed by the PHYprocessing unit 200 depends on the channel bandwidth, the particular MCSbeing utilized, and the guard interval length. For example, in anembodiment, the channel bandwidth determines the number of data tones,and the MCS defines the constellation size, the coding rate, and thenumber of spatial streams utilized. In an embodiment, the guard intervallength determines the total time over which a symbol is transmitted. Forexample, when the SGI has a length of 0.4 μs, the LGI has a length of0.8 μs guard interval, and the data portion 304 has a length of 3.2 μs,the OFDM symbol 300 has a length of 3.6 μs when the SGI is utilized anda length of 4.0 μs when the LGI is utilized.

The number of sub-carriers (or tones) in an OFDM symbol generallydepends on the bandwidth (BW) of the channel being utilized, in someembodiments. For example, an OFDM symbol for a 20 MHz channelcorresponds to a size 64 IDFT and includes 64 tones, whereas an OFDMsymbol for a 40 MHz channel corresponds to a size 128 IDFT and includes128 tones, according to an embodiment. In an embodiment, the tones in anOFDM symbol include guard tones for filter ramp up and ramp down, DCtones for mitigating radio frequency interference, and pilot tones forfrequency offset estimation. The remaining tones can be used to transmitdata (“data tones”), according to an embodiment. More specifically,continuing with the same example, if a size 64 IDFT is used to generatean OFDM symbol, and seven tones are used as guard tones, one tone isused as a DC tone, four tones are used as pilot tones, the remaining 52tones are then used as data tones. As another example, an OFDM symbolfor an 80 MHz channel corresponds to a size 256 IDFT and may include 230data tones according to an embodiment. In general, more tones areavailable for data transmission in higher bandwidth channels resultingin higher data rates generally associated with the wider bandwidths.Various example transmission channels and tone mappings that areutilized in some embodiments of the present disclosure are described inU.S. patent application Ser. No. 12/846,681, entitled “Methods andApparatus for WLAN Transmission”, filed on Jul. 29, 2010, which ishereby incorporated by reference herein in its entirety.

With reference to FIG. 2, a particular MCS defines the coding rate forthe FEC encoders 212, the number of spatial streams created by thestream parser 216, and the number of constellation points used by theconstellation mapper 224, in an embodiment. Generally, higher codingrates, more spatial streams, and larger constellations result in higherdata rates. Conversely, a guard interval (e.g., inserted at unit 244 ofFIG. 2) extends the symbol transmission time, thereby decreasing thedata rate. A longer guard interval decreases throughput more than ashorter guard interval. As a specific example, in an embodiment, a datastream generated using 64-QAM modulation and 5/6 FEC coding rate,transmitted using 8 spatial streams in an 80 MHz channel with a long GI(0.8 μs) is transmitted at approximately 2.3 Gbps. The same data unitbut with a short GI (0.4 μs) is transmitted at approximately 2.5 Gbps.

Referring again to FIG. 2, depending on the particular data rate,different numbers of encoders 212 operate in parallel in variousembodiments and/or scenarios. For example, according to one embodiment,the PHY processing unit 200 includes four encoders 212, and one, two,three, or four encoders operate simultaneously depending on theparticular MCS, bandwidth, and guard interval being utilized. In anotherembodiment, the PHY processing unit 200 includes five encoders 212, andone, two, three, four, or five encoders operate simultaneously dependingon the particular MCS, bandwidth, and guard interval being utilized. Inanother embodiment, the PHY unit 200 includes up to ten encoders 212,and one, two, three, four, five, six, seven, eight, nine or ten encodersoperate simultaneously depending on the particular MCS, bandwidth, andguard interval being utilized. In an embodiment, the number of encodersoperating simultaneously increments at multiples of the data rate, e.g.,every 600 Mbps. In other words, one encoder is utilized for data ratesup to 600 Mbps, two encoders are utilized for data rates between 600Mbps and 1200 Mbps, as an example. In an illustrative example, a datastream encoded with the coding rate of 3/4, modulated using 256-QAMmodulation (with 234 data tones), and transmitted on 4 spatial streamsin an 80 MHz channel requires three encoders 212 to operate in parallel,in an embodiment.

As discussed above, the PHY processing unit 200 (FIG. 2) is utilized toencode and transmit data units, according to an embodiment. In someembodiments, the PHY processing unit 200 is also configured forreceiving and decoding data units. The number of decoders utilized todecode a data stream generally corresponds to the number of encodersused to encode the data stream. Therefore, an AP (such as the AP 14)and/or a client station (such as the client station 25-1) generallyincludes an equal number of encoders and decoders. In some embodiments,however, the number of encoders is different than the number ofdecoders. In an embodiment, the number of decoders operatingsimultaneously increments at multiples of the data rate, e.g., every 600Mbps. In other words, one decoder is utilized for data rates up to 600Mbps, two decoders are utilized for data rates between 600 Mbps and 1200Mbps, as an example. In an illustrative example, a data stream encodedwith the coding rate of 3/4, modulated using 256-QAM modulation (with234 data tones), and transmitted on 4 spatial streams in an 80 MHzchannel requires three decoders to operate in parallel, in anembodiment.

According to an embodiment, for a particular MCS and bandwidth, thenumber of encoders 212 (or decoders) that operate in parallel to encode(decode) a data stream is the same regardless of whether a short guardinterval or a long guard interval is used to generate the symbols.According to another embodiment, for a particular MCS and bandwidth,more encoders (or decoders) are needed to encode (decode) a data streamwith short guard intervals than a data stream with long guard intervals.For example, an MCS that defines a 64-QAM with 6 spatial streams encodedat the rate of 5/6 and transmitted in an 80 MHz channel corresponds to1.725 Gbps data rate when a long guard interval of 0.8 μs is used,according to one embodiment. If the number of encoders (or decoders)increments at 600 Mbps, this data rate then requires three encoders(decoders) to be used in parallel. Continuing with the same example, inthis embodiment, the data rate is approximately 1.9 Gbps when a shortguard interval of 0.4 μs is used. In this case, four encoders (ordecoders) need to operate in parallel to process the data unit. As justanother example, a 80 MHz 64-QAM data stream with coding rate of 5/6 and2 spatial streams requires one encoder (or decoder) when a long guardinterval of 0.8 μs is used, but two encoders (decoders) are needed forthe same MCS and BW when a short guard interval of 0.4 μs is used.Consequently, certain MCSs are supported at the AP 14 and/or the clientstation 25-1 when a long guard interval is utilized, but are notsupported at the AP 14 and/or the client station 25-1 when a short guardinterval is utilized in various embodiments and/or scenarios.

In an embodiment, a client station such as client station 25-1, inestablishing communication with the AP 14, signals to the AP 14 ahighest data rate capability of the client station 25-1 based, at leastin part, on the number of encoders available at the client station toprocess data streams. For example, in establishing communication withthe AP 14, the client station 25-1 transmits an association frame to theAP 14, where the association frame includes an indicator of the highestdata rate of the client station 25-1, according to one embodiment. TheAP 14 then utilizes the indicator of the highest data rate of the clientstation 25-1 to determine whether an SGI or an LGI can be used with aparticular MCS and/or a particular bandwidth when communicating with theclient station 25-1, as will be described in more detail below. Forexample, when a particular MCS at a particular BW and with an SGIresults in a data rate that exceeds the highest data rate of the clientstation 25-1, the AP 14 determines that SGI cannot be used with theparticular MCS and the particular BW, in an embodiment.

In some embodiments, the client station 25-1 also receives an indicationof a highest data rate capability of the AP 14 from the AP 14. Theclient station 25-2 then utilizes the indicator of the highest data rateof the AP 14 to determine whether an SGI or an LGI can be used with aparticular MCS and/or a particular bandwidth when communicating with theAP 14. For example, when a particular MCS at a particular BW and with anSGI results in a data rate that exceeds the highest data rate of the AP14, the client station 25-1 determines that SGI cannot be used with theparticular MCS and the particular BW, in an embodiment.

FIG. 4 is a diagram of a field 400 that is utilized by a firstcommunication device to transmit to a second communication device anindication of a set of one or more MCSs supported by a first device andwhether each of the one or more MCSs is supported when using the SGI,according to an embodiment. The field 400 is included in an associationrequest frame that the client station 25-1 is configured to transmit tothe AP 14, according to an embodiment. In other embodiments, the field400 is included in one or more of a beacon, association request,association response, reassociation request, reassociation response,probe request, and probe response frames or any other initial capabilityinquiry and/or response frame that the station 25-1 is configured totransmit to the AP 14 or vice versa. In some embodiments, the field 400is included in an initial capability inquiry and/or response frame thatthe AP 14 is configured to transmit to the client station 25-1 or viceversa. The field 400 includes an Rx MCS map subfield 402, and an Rxhighest supported data rate subfield 404. According to an embodiment,the Rx MCS map subfield 402 indicates one or more supported MCS sets forone or more of a plurality of spatial streams to be received. Forexample, in an embodiment, one or more supported MCS sets is indicatedfor one or more of up to eight spatial streams to be received. In onesuch embodiment, if a particular device is only able to receive a subsetof the eight spatial streams (e.g., if a device is only able to receive1, 2, 3, or 4 of the 8 spatial streams), the device indicates, in the RxMCS map subfield 402, a supported MCS set for each of the number ofsupported spatial streams, and also indicates that there is no supportfor the remaining numbers of spatial streams. The Rx highest supporteddata rate subfield 404 indicates a highest data rate that the device iscapable of receiving.

Further, the field 400 includes a Tx MCS set defined subfield 406, a TxMCS map subfield 408 and Tx highest supported data rate subfield 410.The Tx MCS set defined subfield 406 indicates whether the subfields 408and 410 are valid. For example, when the Tx MCS set defined subfield 406indicates the subfields 408 and 410 are not valid, a device receivingthe field 400 determines that the device that transmitted the field 400has transmission capabilities according to the subfields 402 and 404.When the Tx MCS set defined subfield 406 is appropriately set, thesubfields 408 and 410 signal the MCS and data rate capabilities of thestation for transmission. The field 400 also includes a reservedsubfield 412.

In another embodiment, the station 25-1 communicates to the AP 14 in oneor more of the association request, association response, reassociationrequest, reassociation response, probe request, probe response, or anyother initial capability inquiry and/or response frame the maximum datarate that the client station 25-1 supports for reception and/or a numberdecoders of the client station 25-1, along with supported MCSs, enablingthe AP 14 to determine the station's SGI capabilities for a particularMCS and/or a particular bandwidth. In yet another embodiment, thestation 25-1 communicates to the AP 14 in one or more of the beacon,association request, association response, reassociation request,reassociation response, probe request, probe response, an indicator ofsupported MCSs for different bandwidths and guard interval lengths (SGIor LGI). In other words, for each supported MCS, the indicator mayindicate whether the client station 25-1 supports that MCS with an SGI.

FIG. 5 is a flow diagram of an example method 500 for generating a dataunit that includes information to indicate transmission and/or receptioncapabilities for a communication device in a wireless network, accordingto an embodiment. With reference to FIG. 1, the method 500 isimplemented by the network interface 16, in an embodiment. For example,in one such embodiment, the PHY processing unit 20 is configured toimplement the method 500. According to another embodiment, the MACprocessing 18 is also configured to implement at least a part of themethod 500. With continued reference to FIG. 1, in yet anotherembodiment, the method 500 is implemented by the network interface 27(e.g., the PHY processing unit 29 and/or the MAC processing unit 28). Inother embodiments, the method 500 is implemented by other suitablenetwork interfaces.

At block 504, a field is generated to indicate a set of one or more MCSssupported by the communication device (by which the method 500 is beingimplemented). The field also indicates whether each of the one or moreMCSs is supported when using a first guard interval. For example, Rx MCSMap field 402 (FIG. 4) is generated to indicate supported MCSs and theRX Highest Supported Data Rate is generated to indicate whether each ofthe supported MCSs is supported by the communication device when a firstguard interval (e.g., the SGI discussed above with reference to FIG. 3)is used. In an embodiment, the field is the field 400 of FIG. 4. Inother embodiments, another suitable field is utilized.

At block 508, a data unit which includes the field is generated. Atblock 512 the data unit is transmitted to another device in the wirelessnetwork. For example, according to an embodiment, the data unit istransmitted to the AP 14 (FIG. 1) in an association request frame oranother suitable data unit. In an embodiment, a processing unit causesthe data unit to be transmitted, such as a PHY processing unit, a MACprocessing unit, or another suitable processing unit.

FIG. 6 is a flow diagram of an example method 600 for determiningcapabilities of a communication device, according to an embodiment. Withreference to FIG. 1, the method 600 is implemented by the networkinterface 16, in an embodiment. For example, in one such embodiment, thePHY processing unit 20 is configured to implement the method 600.According to another embodiment, the MAC processing 18 is alsoconfigured to implement at least a part of the method 600. Withcontinued reference to FIG. 1, in yet another embodiment, the method 600is implemented by the network interface 27 (e.g., the PHY processingunit 29 and/or the MAC processing unit 28). In other embodiments, themethod 600 is implemented by other suitable network interfaces.

At block 604, a first communication device receives a data unit whichincludes capabilities information from a second communication device ina wireless network regarding capabilities of the second communicationdevice. The capabilities information is a field such as the field 400 ofFIG. 4 or another suitable field, according to an embodiment.

At block 608, the first communication device determines one or more MCSsets supported at the second communication device based on theinformation received at block 604. In an embodiment, a supported set isdetermined for each of a plurality of spatial streams.

At block 612, it is determined whether the one or more MCSs in the oneor more of the supported MCS sets are supported at the secondcommunication device when a first guard interval is utilized. In anembodiment, the guard interval support determination is made based on anindication of a highest supported data rate included in the data unitreceived at block 604 (e.g., in the Rx highest data rate subfield 404,FIG. 4). In an embodiment, the first guard interval is a short guardinterval (e.g., the short guard interval discussed above with referenceto FIG. 3).

At block 616, one of the supported MCS s is selected to be utilized whencommunicating with the second communication device.

At block 624, it is determined whether the first guard interval issupported for the selected MCS. If it is determined at block 624 thatthe first guard interval is supported for the selected MCS, then thefirst guard interval is utilized when communicating with the secondcommunication device at block 628. On the other hand, if it isdetermined at block 624 that the first guard interval is not supportedfor the selected MCS, then a second guard interval (e.g., the long guardinterval discussed above with reference to FIG. 3) is utilized whencommunicating with the second communication device at block 628 at block632.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), a programmable logic device (PLD), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed:
 1. A method for determining capabilities of a firstcommunication device in a wireless network, wherein the wireless networkis configured to use a first guard interval between symbols or a secondguard interval between symbols, wherein the first guard interval has alength shorter than a length of the second guard interval, the methodcomprising: analyzing, at a second communication device, a field in adata unit received from the first communication device to determine aset of two or more modulation and coding schemes (MCSs) supported by thefirst communication device and to determine whether one or more MCSs inthe set of two or more MCSs are supported by the first communicationdevice when using the first guard interval, including, analyzing a firstsubfield to determine the set of two or more MCSs supported by the firstcommunication device, and analyzing a second subfield to determine ahighest supported data rate, wherein the highest supported data rateindicates whether each of the two or more MCSs is supported by the firstcommunication device when using the first guard interval; and utilizing,at the second communication device, i) one MCS in the set of two or moreMCSs and ii) the first guard interval a) when communicating with thefirst communication device and b) when it is determined that the one MCSis supported by the first communication device when using the firstguard interval.
 2. A method according to claim 1, further comprising:determining, at the second communication device, a number of encoders ordecoders at the first communication device, wherein the number ofencoders or decoders at the first communication device further indicateswhether each of the two or more MCSs is supported when using the firstguard interval.
 3. A method according to claim 1, wherein analyzing thefield comprises: analyzing the field to determine a set of two or moreMCSs for receiving supported by the first communication device;analyzing the field to determine whether each of the two or more MCSsfor receiving is supported when using the first guard interval;analyzing the field to determine a set of two or more MCSs fortransmitting supported by the first communication device; analyzing thefield to determine whether each of the two or more MCSs for transmittingis supported when using the first guard interval; and wherein utilizingthe one MCS comprises: utilizing i) a first MCS from the set of two ormore MCSs for receiving and ii) the first guard interval a) whentransmitting to the first communication device and b) when it isdetermined that the first MCS is supported by the first communicationdevice when using the first guard interval, and utilizing i) a secondMCS from the set of two or more MCSs for transmitting and ii) the firstguard interval a) when receiving from the first communication device andb) when it is determined that the second MCS is supported by the firstcommunication device when using the first guard interval.
 4. A methodaccording to claim 1, wherein analyzing the field comprises analyzingthe field to determine a set of two or more MCSs supported by the firstcommunication device for different numbers of spatial streams.
 5. Amethod according to claim 1, further comprising: selecting, at thesecond communication device, the one MCS from the set of two or moreMCSs; and determining, at the second communication device, whether theone MCS is supported by the first communication device when using thefirst guard interval.
 6. A method according to claim 5, furthercomprising: utilizing, at the second communication device, i) the oneMCS and ii) the second guard interval a) when communicating with thefirst communication device and b) when it is determined that the one MCSis not supported by the first communication device when using the firstguard interval.
 7. An apparatus for use in a wireless network, whereinthe wireless network is configured to use a first guard interval betweensymbols or a second guard interval between symbols, wherein the firstguard interval has a length shorter than a length of the second guardinterval, the apparatus comprising: a wireless network interface havingone or more integrated circuits configured to analyze a field in a dataunit received from a communication device to determine a set of two ormore modulation and coding schemes (MCSs) supported by the communicationdevice and to determine whether one or more MCSs in the set of two ormore MCSs are supported by the communication device when using the firstguard interval, including, analyzing a first subfield to determine theset of two or more MCSs supported by the communication device, andanalyzing a second subfield to determine a highest supported data rate,wherein the highest supported data rate indicates whether each of thetwo or more MCSs is supported by the communication device when using thefirst guard interval, and utilize i) one MCS in the set of two or moreMCSs and ii) the first guard interval when communicating with thecommunication device and when it is determined that the one MCS issupported by the communication device when using the first guardinterval.
 8. An apparatus according to claim 7, wherein the one or moreintegrated circuits are configured to determine a number of encoders ordecoders of the communication device, wherein the number of encoders ordecoders of the communication device further indicates whether each ofthe two or more MCSs is supported when using the first guard interval.9. An apparatus according to claim 7, wherein the one or more integratedcircuits are configured to analyze the field to determine a set of twoor more MCSs for receiving supported by the communication device,analyze the field to determine whether each of the two or more MCSs forreceiving is supported when using the first guard interval, analyze thefield to determine a set of two or more MCSs for transmitting supportedby the communication device, analyze the field to determine whether eachof the two or more MCSs for transmitting is supported when using thefirst guard interval, utilize i) a first MCS from the set of two or moreMCSs for receiving and ii) the first guard interval a) when transmittingto the communication device and b) when it is determined that the firstMCS is supported by the communication device when using the first guardinterval, and utilize i) a second MCS from the set of two or more MCSsfor transmitting and ii) the first guard interval a) when receiving fromthe communication device and b) when it is determined that the secondMCS is supported by the communication device when using the first guardinterval.
 10. An apparatus according to claim 7, wherein the one or moreintegrated circuits are configured to analyze the field to determine aset of two or more MCSs supported by the communication device fordifferent numbers of spatial streams.
 11. An apparatus according toclaim 7, wherein the one or more integrated circuits are configured to:select the one MCS from the set of two or more MCSs, and determinewhether the one MCS is supported by the communication device when usingthe first guard interval.
 12. An apparatus according to claim 11,wherein the one or more integrated circuits are configured to: utilizei) the one MCS and ii) the second guard interval a) when communicatingwith the communication device and b) when it is determined that the oneMCS is not supported by the communication device when using the firstguard interval.
 13. A non-transitory, tangible computer readable mediumor media storing instructions that, when executed by one or moreprocessors, cause the one or more processors to: analyze a field in adata unit received from a communication device to determine a set of twoor more modulation and coding schemes (MCSs) supported by thecommunication device and to determine whether one or more MCSs in theset of two or more MCSs are supported by the communication device whenusing a first guard interval, including, analyzing a first subfield todetermine the set of two or more MCSs supported by the communicationdevice, and analyzing a second subfield to determine a highest supporteddata rate, wherein the highest supported data rate indicates whethereach of the two or more MCSs is supported by the communication devicewhen using the first guard interval, and a wireless network includingthe communication device is configured to use the first guard intervalbetween symbols or a second guard interval between symbols, wherein thefirst guard interval has a length shorter than a length of the secondguard interval; and cause a network interface device to utilize i) oneMCS in the set of two or more MCSs and ii) the first guard interval a)when communicating with the communication device and b) when it isdetermined that the one MCS is supported by the communication devicewhen using the first guard interval.
 14. A non-transitory, tangiblecomputer readable medium or media according to claim 13, further storinginstructions that, when executed by one or more processors, cause theone or more processors to: analyze a first subfield to indicate the setof two or more MCSs supported by the communication device; and determinea number of encoders or decoders at the communication device, whereinthe number of encoders or decoders at the communication device furtherindicates whether each of the two or more MCSs is supported when usingthe first guard interval.
 15. A non-transitory, tangible computerreadable medium or media according to claim 13, further storinginstructions that, when executed by two or more processors, cause theone or more processors to: analyze the field to determine a set of twoor more MCSs for receiving supported by the communication device;analyze the field to determine whether each of the two or more MCSs forreceiving is supported when using the first guard interval; analyze thefield to determine a set of two or more MCSs for transmitting supportedby the communication device; analyze the field to determine whether eachof the two or more MCSs for transmitting is supported when using thefirst guard interval; cause the network interface device to utilize i) afirst MCS from the set of two or more MCSs for receiving and ii) thefirst guard interval a) when transmitting to the communication deviceand b) when it is determined that the first MCS is supported by thecommunication device when using the first guard interval; and cause thenetwork interface device to utilize i) a second MCS from the set of twoor more MCSs for transmitting and ii) the first guard interval a) whenreceiving from the communication device and b) when it is determinedthat the second MCS is supported by the communication device when usingthe first guard interval.
 16. A non-transitory, tangible computerreadable medium or media according to claim 13, further storinginstructions that, when executed by one or more processors, cause theone or more processors to: analyze the field to determine a set of twoor more MCSs supported by the communication device for different numbersof spatial streams.
 17. A non-transitory, tangible computer readablemedium or media according to claim 13, further storing instructionsthat, when executed by one or more processors, cause the one or moreprocessors to: select the one MCS from the set of two or more MCSs; anddetermine whether the one MCS is supported by the communication devicewhen using the first guard interval.
 18. A non-transitory, tangiblecomputer readable medium or media according to claim 17, further storinginstructions that, when executed by one or more processors, cause theone or more processors to: cause the network interface device to utilizei) the one MCS and ii) the second guard interval a) when communicatingwith the communication device and b) when it is determined that the oneMCS is not supported by the communication device when using the firstguard interval.